Gas turbine engines are internal combustion engines typically used to provide thrust to an aircraft or to provide power for land-based operations. A gas turbine engine may consist of a fan section surrounded by a fan containment case, a compressor section, one or more combustors, and a turbine section. Air may be drawn into the engine and accelerated by the rotating blades of the fan section, and it may be subsequently compressed/pressurized in the compressor section prior to entry into the combustor(s). Once in the combustor(s), the air may be mixed with fuel and combusted to generate hot combustion gases. Energy may then be extracted from the combustion gas products in the turbine section to power the turbine section, the compressor section, and the fan section. The combustion gas products may then be expelled through an exhaust nozzle of the engine to provide forward thrust for aerospace applications, or to provide power for other applications.
During the testing and development of new gas turbine engines, various types of instrumentation may be mounted on the fan containment case for testing engine operation. Some testing systems may require the use of arrays of instruments mounted on the fan case, with each of the instruments extending into the outer flowpath of the fan section. For example, in one testing system, a pair of probes may be mounted on the fan case forward and aft of a fan blade to monitor the position and rotation of the blade. Due to the curved shape of the fan blades, optimal readings in this system often requires the instruments to be inserted through the wall of the fan case at off-axis angles that deviate from perpendicular to the outer surface of the fan case. However, as many recent gas turbine engine designs use composite-based fan containment cases, the formation of off-axis cuts through the composite fan cases for mounting the instruments has presented a significant challenge as off-axis cuts may damage the composite materials of the fan case.
To enable the mounting of instrumentation features on composite fan cases, US Patent Application Publication Number 2013/0336773 describes the use metallic rails with instrument holders mounted on a band of sacrificial composite material circumscribing the outer surface of the fan case. The sacrificial composite material reinforces the fan case and allows the drilling of a hole through the composite fan case. While effective, it is not disclosed whether the metallic rails support the mounting of instruments at off-axis angles. Moreover, space may be limited for such metallic rails on fan cases due to instrumentation trays or other external components.
Clearly, there is a need for improved systems for mounting instruments on composite fan cases of gas turbine engines.